Technical Field
The present invention is related to thin double-structured composite anti-corrosion coatings and to a method of preparing such anti-corrosion submicrometer thickness coatings for metal surfaces, in particular for application to anodizable metals.
Background Art
Corrosion resistant or anti-corrosion coatings find application in many industries, in particular in: a) aero-space industry, b) car-industry, and c) medical implants and instruments producing industries. Other applications include: metal industry producing equipment, tools and aid for chemical and food industries, for (sustainable) energetics, for building industry, etc.
It is desirable for such coatings to be hard, to protect the substrate and also elastic, for example so that the coating does not flake off.
In the state of the art U.S. Pat. No. 7,323,230 B2 “Coating for aluminum component” by T T Doan, K K-T Ngan (Applied Materials, Inc.), priority date Feb. 2, 2006 describes a method consisting principally of three stages: a) anodizing the substrate, b) Chemical Vapour Deposition (CVD) deposition of Al film and c) “re-flow the Al film”, oxidation of aluminum and deposition of alumina to the anodized layer; stages b and c together give a CVD-like process; they claim also equipment for the topmost alumina coating.
Another technical solution is described in United Kingdom Patent GB2455993 “Article coated by ALD and CVD/PVD”, by P. Peeters, R. Tietema (Hauzer Techno Coating; CORRAL partner), priority date Dec. 28, 2007. This patent claims 2-layer coating done by ALD and CVD/PVD (Physical Vapour Deposition) in arbitrary order, and equipment for that. The technical object of said 2-layer coating is to provide a way of protecting articles having PVD or CVD layer from the effect of poor adhesion and/or corrosion and retaining the positive physical benefits of named layers such as high hardness, high resistance to wear, low coefficient of friction etc. In addition, the object of said 2-layer coating is to facilitate giving a coated article a desired coloured appearance when illuminated. However, when the first coating layer is made by ALD this layer, and therefore the whole coating, has poor adhesion. If the first layer is made by PVD/CVD then the first layer must be several micrometers or thicker to obtain a low-density of defects in the layer, and to screen electrically the influence of electrochemically active phases in near-surface area of the article to prevent localized galvanic corrosion.